Galactic hitchhikers visiting our solar system, if they
exist, would probably love to get their hands on a new guide that puts GPS to
shame.

A planetary scientist has made the most detailed maps of our
local planets, moons and asteroids yet by combining hundreds of spacecraft
images to chart all the nooks and crannies of numerous surfaces, including the
asteroids Phobos, Itokawa and Eros. Upcoming targets for mapping include the
planet Mercury and eight of Saturn's moons, such as frozen
Enceladus with its icy geysers, as well as Earth's moon.

"I have three computers crunching away right now,"
said Robert Gaskell, a planetary scientist based in Altadena, Calif., who works
at the Planetary Science Institute. "One's working on the moon, one's
working on Eros, and another's working on Mercury."

?Gaskell uses many images from different angles and
illuminations to figure out the slopes and heights of alien terrains, whether a
rocky asteroid or icy moon. His method of stereo-photo-clinometry (SPC) creates
square "maplets" on a computer model of the target, and smaller
squares get added as the model receives more detailed data.

A major project involves creating highly accurate maps of
the entire surface of Mercury  the closest planet to the sun  based on an
expected stream of images from NASA's MESSENGER
spacecraft. The probe still needs to swoop past Earth and Venus before
settling into a Mercury orbit in 2011.

"Doing the larger bodies like the moon and Mercury,
you've got to make an awful lot of maplets," Gaskell told SPACE.com.
He added that Mercury alone would probably involve 500,000 maplets of varying
size.

Gaskell has already begun combining images from an initial
MESSENGER flyby
of Mercury in January with older Mariner 10 images taken in 1973. But the
three Mariner 10 flybys produced photos from the same sun angle, which means
Gaskell only has two angles to work with at the moment.

"It won't be until we get overlapping data from
different sun directions that it will really start making a lot of sense,"
Gaskell said. "It does give a reasonable solution now, but I don't
completely trust it."

Other map work need not wait until MESSENGER settles into
its Mercury orbit in 2011. NASA also wants Gaskell to map eight of the moons
orbiting Saturn's ringed visage, including Enceladus.

Mission planners may use the maps as navigational tools for
the Cassini spacecraft to revisit Enceladus in October, where a fresh flyby may
provide additional data on the moon's
geysers.

The accurate map modeling could also help scientists study
Saturn's moons for signs of frozen tidal stresses that might reflect the
satellites' orbital histories, when they gravitationally tugged at one another
in more unpredictable ways.

Gaskell's earlier work has already garnered a NASA
Exceptional Achievement Medal. The award recognized the maps of the asteroid
Itokawa as "the highest resolution description of an asteroid,"
at resolutions better than 15.75 inches (40 cm).

The scientist's computers continue working around the clock,
but thousands of planetary and other bodies still remain in the solar system.